Gas turbine engines are used as the primary power source for many types of aircraft. Most turbine engines include rotating components such as a fan, a compressor, and a turbine. The rotating components may be clamped together either by a tieshaft or bolted flange joints to form a rotor group. Two or more bearing assemblies may be employed to support the rotor group. Generally, the bearing assemblies may be surrounded by a support housing, which may be connected to an engine case.
During high-speed rotation of the rotor group, forces may be transmitted from the rotor group to the support housing. To damp the effects of the transmitted forces, a squeeze film damper may be included in some engines. A squeeze film damper operates by supplying fluid (usually oil) through dedicated oil delivery passages into a squeeze film cavity formed via a clearance between the support housing and the bearing assemblies.
Although squeeze film dampers are relatively useful in reducing rotor vibration in some cases, they may suffer drawbacks in others. For example, because the rotor orbiting within the mount itself may become off-center with respect to the squeeze film cavity, the rotating rotor group may not remain concentric. Thus, the rotor may sit at the bottom of the damper clearance or may be unable to process around the clearance between the bearing assembly and the support housing. As a result, the squeeze film damper may become relatively stiff during operation and may not absorb as much vibration as desired. Additionally, the support housing stiffness may allow the rotor group to vibrate with certain modes when subjected to a particular engine operating speed range, and the squeeze film damper may not adequately damp this increased rotor unbalance response.
Hence, it is desirable to have an apparatus that may be used to improve the damping capabilities of an off-center squeeze film damper and provide a support structure stiffness that minimizes a rotor-to-structure unbalance response. It is desirable for the apparatus to be capable of limiting rotor radial excursion and to accommodate a particular rotor thrust load. It is also desirable for the apparatus to have a relatively compact design and to be capable of being retrofitted into existing engines.